Method for the production of samarium alloys



Patented Aug. 18., 1970 3,524,800 METHOD FOR THE PRODUCTION OF SAMARIUM ALLOYS Edward Morrice, Jr., James E. Murphy, and Thomas A. Henrie, Reno, Nev., assignors to the United States f America as represented by the Secretary of the Interior No Drawing. Filed Apr. 4, 1968, Ser. No. 718,908

Int. Cl. C22d 3/20 US. Cl. 204-71 3 Claims ABSTRACT OF THE DISCLOSURE Samarium is electrodeposited from a Sm O source onto a consumable iron, nickel or cobalt cathode to produce a samarium alloy. The samarium is then separated from the alloy by vacuum sublimation.

This invention, which relates to the preparation of samarium metal and samarium alloys, resulted from work done by the Bureau of Mines in the US. Department of the Interior, and domestic title to the invention is in the Government.

Due to expanding metallurgical uses for samarium metal, especially its use as an excellent magnetic material when alloyed with cobalt, the production of high purity samarium metal has become very desirable. However, much difliculty has heretofore been encountered in preparing the metal in a form suitable for such uses. Attempts to electrowin samarium from its oxide have not been successful because reactions between the samarium and electrolyte have occurred. Reduction of samarium halide has met with little success. Some samarium has been produced by reducing the oxide thereof with lanthanum under a vacuum, but this has resulted in the samarium product having undesirable amounts of lanthanum and oxygen.

We have now discovered that high purity samarium metal can be produced by (1) electrodepositing samarium from a Sm O source onto an iron, nickel or cobalt cathode to produce a samarium alloy with the cathode metal, and (2) separating samarium from the alloy by vacuum sublimation (distillation). The term sublime (or sublimation), as used throughout the specification and claims, means that the samarium passes from the solid to the gaseous state, and again condenses to solid form, without apparently liquefying.

It is therefore an object of this invention to convert Sm O to high purity elemental samarium. Another object is to electrowin samarium from its oxide. A further object is to produce samarium alloys with iron, nickel and cobalt. A still further object is to separate samarium from an alloy of samarium and another metal selected from the group consisting of iron, nickel and cobalt. Other objects and advantages will be obvious from the following detailed description of the invention.

In the practice of the invention, samarium sesquioxide ($111 0 is dissolved in a molten salt electrolyte while a current is passed therethrough by means of a carbon (graphite) anode and a cathode which is composed of iron, nickel or cobalt. During electrolysis, the molten bath is maintained at a temperature below the melting reactive cathode allows the samarium to be electrowon from its oxide without the samarium having time to react with electrolyte.

An electrolyte composed of SmF and another fluoride selected from the group consisting of LiF, BaF CaF MgF or SrF is particularly suitable for the purposes of invention. In such a mixture, the SmF is preferably present in amounts ranging from about 40 to about weight percent of the electrolyte.

Solidified samarium-cathode metal alloy, which is recovered from the electrodeposition step, is then heated under a vacuum of about 10- to about 10" torr to a temperature suflicient to sublime samarium. This temperature is about 800 C. to about 900 C. for a samarium-iron alloy; about 1100 C. to about 1200 C. for samarium-nickel; and about 1100 C. to about 1200 C. for samarium-cobalt. During sublimation samarium vapors are collected in solid form on a cooled surface composed of a material (e.g., tantalum, tungsten or molybdenum) from which the samarium metal may be easily separated by peeling.

The following example specifically illustrates a way in which the invention has been carried out:

A mixture of 81 weight percent SmF and 19 weight percent LiF powders was melted in a graphite crucible inside a chamber having an inert atmosphere. Anelectrode arrangement consisting of two carbon anodes and one iron cathode was submerged in the fluoride melt. Temperatures in the range of 900 C. to 1,000 C. required for preparing the molten samarium-iron alloy were maintained by internally heating the electrolyte by passing alternating current between the anodes. Samarium sesquioxide was added to the fluoride melt during electrolysis. As the iron cathode was consumed the section thereof external to the bath was slowly immersed in the electrolyte. After completion of electrolysis, the bath was allowed to freeze and the samarium-iron nodules recovered. Operational data during electrolysis are given in the following table.

Sm O added to fluoride bath43 grams Consumable iron cathode fed to electrolyte-8 grams Average direct current-52 amp Average D.C. voltage23 volt Average alternating current 69 amp Average A.C. voltage-41 volt Initial anode current density (D.C.)0.5 amp/cm. Initial anode current density (A.C.)--1.4 amp/cm. Average electrolyte temperature--960 C.

Average cell bottom temperature-580 C. Duration of electrolysis-1.5 hr.

Sm-Fe alloy recovered68 grams Current efliciency4l percent 1 Supplemental power applied to the anodes.

The composition of the samarium-iron nodules recovered after electrolysis varied from 12 to 2.0 weight percent iron. (When cobalt or nickel was used as the cathode under similar operating conditions, the alloy ranged from 20 to 30 weight percent cobalt or nickel.)

Sublimation of the samarium was then accomplished by heating the alloy nodules to a temperature of 800 900 C. in a crucible under a vacuum of 10- to 10 torr. Sublimed samarium metal was collected on a tungsten metal cover placed directly above the crucible. The samarium deposit consisted of a substantial layer of metal and was easily separated from the cover by peeling away tungsten. Samarium recovery from the alloy was of the order of 60 percent. Analysis of samarium metal product showed l00 p.p.m. oxygen, 10 p.p.m. carbon, and 10 p.p.m. iron. Other rare-earths, including lanthanum, were not detected by spectrographic or X-ray analysis.

By the present invention, samarium metal is produced in more pure form than that available by standard comthanum contamination and a high cost reductant are eliminated. As such, the pure samarium produced by the invention is a desirable alloying element for other metals. Also, the intermediate alloy product, particularly the co balt alloy, is a valuable material in itself.

Although the particular process herein described is well adapted to carry out the objects of the present invention, it is to be understood that various modifications and changes may be made all coming within the scope of the following claims.

What is claimed is:

1. A proces for treating Sm O comprising:

(a) electrodepositing samarium metal from a $111 source onto a cathode selected from the group consisting of iron, nickel and cobalt; said electrodeposition being carried out in a molten electrolyte maintained at a temperature below the melting point of 4 said cathode metal but above the melting point of samarium-cathode metal alloy which forms during electrodeposition on said cathode; and

(b) separating out said alloy.

2. The process of claim 1 in which said molten electrolyte is a mixture of SmF and another fluoride selected from the group consisting of LiF, BaF CaF MgF and SI'FZ. 3. The process of claim 2 in which said another fluoride is LiF, and wherein said SmF is present in said electrolyte in an amount of about weight percent to about weight percent of said electrolyte.

References Cited UNITED STATES PATENTS 5/1968 Wood 20471 1/1967 Henrie et al 204-71 US. Cl. X.R. 75-63, 134, 

